This invention relates to a method for the automatic digital measurement of vertex dioptric power.
Methods are already known for the analog measurement of vertex power in which the refractive power of spectacle lenses is measured, generally semi-automatically, by operating personnel. The work of such personnel includes, among other things, the centering of the spectacle lenses and the reading of measurement value. Should the measurement value lie outside of predetermined tolerances, the lens in question is sorted out by the operator.
From West German Pat. No. 1,125,680, a measurement device is known with which vertex dioptric powers can also be measured. In using said measurement device, the lens to be tested is placed in the parallel-ray path of an optical system, and one measures the consequent displacement of the focal plane in the direction of the optical axis; the vertex refractive powers can be calculated from this measurement. A detector placed in said plane continuously tracks the focal plane; its signals serve for the automatic centering of the object being tested.
The method of the known device employs chopped light and requires, in addition to the drives for the centering movement, an accurately operating tracking control which retains the detector in the focal plane. The measurement of toric lenses requires the detector to be positioned into two focal planes, in the course of rotating the object being examined. Thus, the known method requires a large amount of apparatus and consumption of time.